Fiber dispersion and breakage in deep screw channel during processing of long fiber-reinforced polypropylene

Long glass fiber-reinforced thermoplastics are usually processed by pultruded granules, but glass fiber rovings were used to process long glass fiber-reinforced thermoplastics in this study. This article investigated the dispersion and breakage of fibers during extrusion processing of long glass fiber-reinforced polypropylene containing 30 wt% glass fibers at a certain processing conditions. For this study, the morphology of the surface and polished cross-section of helices was observed by digital photography, as was the morphology of the remaining fiber after burning. On this basis, the fiber/polymer system behavior in the screw channel and the dispersion mechanism of the fiber bundles were analyzed. Moreover, scanning electron microscopy (SEM) was used to observe individual fiber cross-sections to analyze the mechanism of fiber breakage. Finally, the effect of processing conditions such as temperature, screw speed and fiber content on fiber length and dispersion was studied. The results show that the fiber agglomerates composed of fiber bundles form near the barrel surface at the fiber feed point and then undergo three main stages: compression, impregnation, and dispersion. The fiber bundles separate into daughter bundles and individual fibers in different parts of the screw channel. In addition, the results indicate that the fibers can suffer tensile fracture and bending fracture during the extrusion processing. Finally, this paper includes suggestions for improving fiber bundle dispersion and reducing fiber breakage.